Discharge cell for ozonizer

ABSTRACT

Decrease in the ozone concentration that becomes a problem when high purity oxygen is used as a raw material gas is prevented. A high purity alumina substrate having a high screen degree is used as a dielectric. A catalytic substance to hinder the decrease of the ozone concentration is fixed on the surface of the alumina substrate as the dielectric by a baking fixing agent. The baking fixing agent is a glass that becomes a paste form that is capable of powder kneading the catalytic substance and attaching to the surface of the dielectric, fixes the catalytic substance on the surface of the dielectric by hardening by baking, and shows ozone resistance and sputtering resistance under the production of ozone in the discharge gap, and forms a functional film containing a large amount of the catalytic substance and is stable on the surface of the dielectric.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a discharge cell used in a discharge type ozonizer, and in more detail, relates to a discharge cell for an ozonizer that is capable of bringing out the maximum ability of the ozonizer even in the case where nitrogen is not added or a small amount of nitrogen is added into the raw material gas.

2. Description of the Related Art

Discharge cells used in a discharge type ozonizer, called as an ozonizer, are roughly divided into a plate type and a tube type. Each of the discharge cells have a pair of electrodes arranged with a gap therebetween, and have a configuration in which a dielectric is arranged between the electrodes so as to contact at least one of the electrode surfaces of the pair of electrodes to form a discharge gap between the electrodes. Ozone gas is produced by circulating a raw material gas such as oxygen in the discharge gap with a condition in which a silent discharge is generated by applying a prescribed high frequency high voltage in the discharge gap.

Recently, a configuration has emerged in which a pair of dielectrics is arranged inside each pair of electrodes and the discharge gap is formed between the pair of dielectrics in order not to expose the electrodes consisting of metal to the discharge gap. Furthermore, by considering this as one unit, a multi-layer structure is often used in which a plurality of the units is layered in the thickness direction.

The dielectrics in the discharge cell are roughly divided into a substrate type having rigidity in shape and a coated type in which the surface of the gap side of the electrode having rigidity is coated. In the case of the coated type, there is a problem such that non-uniformity of the thickness distribution cannot be avoided and this leads to non-uniformity of the gap amount of the discharge gap, and the substrate type such as a ceramic plate that is hard and has chemical resistance has recently becoming the mainstream.

Incidentally, the ozonizer has begun to be used broadly in semiconductor manufacturing equipment while being used in various chemical processing equipment. In the case of an ozonizer for semiconductor manufacturing used in formation of an oxide film, ashing of a resist, cleaning of a silicon wafer, and the like, there is a necessity of generating pure ozone gas with extremely low contamination (metal impurities and particles, abbreviated as contami below) because high cleanliness is demanded, and because of this, oxygen gas with high purity is used as the raw material gas.

Further, the configuration in which a pair of dielectrics are arranged inside each pair of electrodes and the discharge gap is formed between the pair of dielectrics as described above is adopted as a structure of the discharge cell in order not to expose the electrodes consisting of metal to the discharge gap. A high purity alumina substrate having high mechanical strength and superior in ozone resistance and sputtering resistance is recommended as the dielectric here, especially a dielectric of the substrate type from the viewpoints of maintaining cleanliness, and the like.

Furthermore, from the necessity of producing high concentrated ozone gas, decreasing the gap amount in the discharge gap and making it uniform are attempted together with making high purity oxygen gas, and a gap amount decreased to 0.2 mm or less can be found at present.

In the case of using high purity oxygen gas as the raw material gas, a problem has been known widely in which ozone concentration of ozone gas rapidly decreases right after the operation is started and the prescribed performance is not exhibited. In order to solve this problem, adding a catalyst gas to the high purity oxygen gas is considered to be effective, and high purity nitrogen gas that is easily obtained in a semiconductor manufacturing process is often used as the catalyst gas.

The case where the dielectric is the above-described high purity alumina substrate is also not an exception, and performance as an ozonizer is hardly exhibited in the case where the raw material gas is high purity oxygen gas. On the contrary, in the case of a high purity alumina substrate, it has been found that the ozone concentration does not increase sufficiently even when nitrogen gas is mixed into the oxygen gas. In more detail, in the case of arranging a high purity alumina substrate on both surface sides of the discharge gap, especially the effect of adding catalyst gas can not be obtained sufficiently. This is considered to be because impurities are extremely removed from the surface of the dielectric contacting with the discharge gap.

From such circumstances, attempts of increasing the ozone concentration without using a catalyst gas have proceeded in every direction, one of the attempts is to use a functional substance in the dielectric, and using titanium oxide as the functional substance is described in Japanese Patent Application Laid-Open (JP-A) No. 11-21110 and JP-A No. 2005-350336. Further, effectiveness of a tungsten substance as the functional substance is described in U.S. Pat. No. 5,932,180 and JP-A No. 2005-320223.

When the countermeasures described in JP-A Nos. 11-21110 and 2005-350336, U.S. Pat. No. 5,932,180 and JP-A No. 2005-320223 are roughly divided from a viewpoint of a fixing method of the functional substance to the dielectric, there are two methods including a method of mixing into the dielectric and a method of coating onto the surface of the dielectric, that is, formation of a functional film on the surface of the dielectric. For example, in the case where the functional substance is titanium oxide, in order to achieve a high effect by mixing, mixing of 10% by weight or more, desirably about 50% by weight becomes necessary. In the case where the dielectric is an alumina substrate, when such large amount of additive is added, sintering becomes difficult, strength of the substrate remarkably decreases, and manufacturing itself may become impossible depending on the case. Because of this, an added amount of the functional substance is limited, and an effect toward the ozone concentration becomes insufficient.

Stating further, an alumina substrate having a purity of 99.5% has been widely on the market for example as an alumina substrate with less impurities. When the functional substance is mixed into the dielectric, such alumina substrate on the market cannot be used, and a separately made substrate becomes necessary. Because of this, there is a practical problem that the cost of the dielectric raises remarkably. The reason that the content becomes large in the case of mixing the functional substance into the dielectric is that the exposure amount of the functional substance on the surface of the dielectric has to be secured at a certain amount or more, and because of this, its content cannot help being large naturally.

On the other hand, coating of the functional substance onto the surface of the dielectric substrate has an advantage that a large amount of the functional substance on the surface of the dielectric can be secured, and a functional film with 100% of the functional substance can be formed on the entire surface of the dielectric with flame spraying or vapor deposition. However, in the flame spraying or the vapor deposition of the functional substance, surface roughness of the functional film formed on the surface of the dielectric becomes large and management of the film thickness is difficult, and unevenness of the distribution of the gap amount in the discharge gap becomes large. This becomes a cause of decrease of the ozone concentration. Further, a high cost required in the coating becomes a problem. Furthermore, the functional film formed with flame spraying or vapor deposition is easily peeled because it is in the state of simply being placed on the surface of the dielectric. When the functional film is peeled, not only the contami is generated, but also the primary effect by the functional substance decreases, and unevenness is generated on the surface of the dielectric and it becomes a cause of decreasing the ozone concentration.

Further, in order to give a small and uniform gap amount in the discharge gap, a rib may be formed on the surface of the dielectric with a glass substance, or the like (refer to JP-A No. 2005-68003). In the case of forming a film of the functional substance on the surface of the dielectric with flame spraying or vapor deposition, a film of the functional substance is formed on the entire surface of the dielectric, and then a rib is formed on top of the film. Because the functional film consisting of the functional substance is easily peeled, there are problems that the formation of the rib is difficult and that the formed rib is peeled when the rib is formed on top of the film. That is, a rib to secure the gap amount is required to be formed directly on the high purity alumina substrate that is the main body of the dielectric.

Moreover, in the case where the functional substance is a tungsten substance, in U.S. Pat. No. 5,932,180, metal tungsten is applied on the surface of the dielectric. However, this metal tungsten is changed to a tungsten oxide (WO₃) due to a strong oxidation power of ozone produced in the discharge gap, and this WO₃ is considered to actually cover the surface of the dielectric. Incidentally, WO₃ is an insulator.

Further, in JP-A No. 2005-320223, a conductive tungsten oxide having a prescribed resistivity is applied on the surface of dielectric contacting the discharge gap and the surface of the electrodes. Among tungsten oxides, WO₃ is an electric insulator. However, WO₂ has good conductivity, and the resistivity of the tungsten oxide can be actually changed by changing the oxygen amount. However, because this conductive tungsten oxide also contacts with the discharge gap and directly contacts to ozone, WO_(x) (x<3) is also considered to change to WO₃ that is an insulator when it is used.

That is, although expression of the technique described in Reference Document 3 and the technique described in Reference Document 4 differs from each other, WO₃ is considered to be applied as a catalytic substance on the surface contacting the discharge gap in the discharge cell that is used actually.

SUMMARY OF THE INVENTION

An objective of the present invention is to provide a discharge cell for an ozonizer that can effectively prevent a decrease of ozone concentration in the case where nitrogen is not added or a small amount of nitrogen is added while avoiding peeling of a functional substance from the surface of a dielectric and a harmful influence to a rib for forming a gap without mixing the functional substance into the dielectric.

In order to achieve the above-described objective, the present inventors devotedly investigated a method of effectively fixing the functional substance on the surface of the dielectric by giving up mixing of the functional substance into the dielectric and focusing on the application of the functional substance onto the surface of the dielectric. That is, using a less expensive product on the market such as a high purity alumina substrate as the dielectric, a new method replacing flame spraying and vapor deposition as a means of attaching and fixing the functional substance on the surface was investigated from various angles. As a result, the following facts were discovered.

In the application technique of the functional substance up until now, the technique has been developed by attaching the functional substance itself on the surface of the dielectric. Typical examples are flame spraying and vapor deposition. However, most of the functional substances are primarily a fine powder as seen in titanium oxide. In the flame spraying and the vapor deposition, film formation is performed using a target obtained by sintering a fine powder of the functional substance. However, it is as described above that the functional film formed in such a manner has many problems.

Accordingly, the present inventors concentrated their power into development of a fixing means by converting a concept into a direction of fixing a fine powder of the functional substance as it is onto the surface of the dielectric. As a result, it was discovered that a large amount of the functional substance can be fixed stably onto the surface of the dielectric by mixing the fine powder of the functional substance into a glass paste, attaching it onto the surface of the dielectric, and baking. Further, at the same time, it became clear that changes in quality due to ozone and sputtering, and generation of contami due to the sputtering can be suppressed by selecting a composition of the paste, that adjustment of the film thickness is easy by using screen printing or the like, and formation of a thin film such as those having a thickness of a few μm is possible, that a film formation avoiding a part of a rib for forming a gap is possible and a harmful influence is not given to the rib, and the like.

The discharge cell for an ozonizer in the present invention is developed with such knowledge as a basis and in which an ozonizer contains a dielectric arranged to contact at least one of the electrodes in order to form a discharge gap for generating ozone between a pair of the electrodes, and a functional substance to hinder a decrease of the ozone concentration is fixed on the surface of the dielectric by a baking fixing agent showing ozone resistance and sputtering resistance under ozone production in the discharge gap.

In the discharge cell for an ozonizer in the present invention, a functional substance such as titanium oxide or tungsten oxide is fixed on the surface of the dielectric in a film form in a powder state by a baking fixing agent. By this, a functional film containing a large amount of the functional substance exceeding 50% by weight is stably formed on the surface of the dielectric, and an effect of preventing decrease of the ozone concentration by a functional substance can be exhibit to the full. On top of that, for example, an alumina substrate on the market of 99.5% purity can be used as it is as the dielectric. Furthermore, because the baking fixing agent shows ozone resistance and sputtering resistance, there is almost no fear that the fixing agent itself becomes a source of contami.

The functional substance is a metal or its oxide M_(x)O_(y) (M is a metal element), specifically it is a metal such as Ti, W, Sb, Mn, Fe, Co, Ni, V or Zn, or an oxide of these metals (for example, TiO₂, WO₂, WO₃, Sb₂O₃, Mn₃O₄, Fe₂O₃, CO₃O₄, NiO, V₂O₅, and ZnO), and these powders can be used alone or in a mixed state. The particle size of the powder is preferably 0.1 to 10 μm on average. This is because the film thickness of the functional film is about 10 μm as described later, its powder is required to be finer than this, and on the other hand, handling of an extremely fine particle becomes difficult.

The baking fixing agent is preferably a substance that is in a form of a paste that is capable of powder kneading the functional substance and attaching to the surface of the dielectric, and that shows ozone resistance and sputtering resistance under the production of ozone in the above-described discharge gap in addition to fixing the functional substance onto the surface of the dielectric by hardening with baking. Typical baking fixing agent is a glass, specifically a SiO₂—Al₂O₃—B₂O₃ glass is preferable, and among these, a glass is especially preferable in which the amount of SiO₂ is 60 to 70% by weight, the amount of Al₂O₃ is 1 to 10% by weight, and the amount of B₂O₃ is 10 to 20% by weight. When the glass is used, it is in a fine powder state, it becomes in a paste state by mixing with a binder called a vehicle in which a resin is dissolved by a solvent, and the film formation and control of the film thickness are made easy by making this into a paste by mixing with a fine powder of the functional substance and making screen printing and the like onto the surface of the dielectric possible. By baking, a glass powder in the paste becomes amorphous and the binder disappears, and as a result, a solid thin functional film in which a fine powder of the functional substance is dispersed and mixed into the glass is formed on the surface of the dielectric.

The particle size of the glass powder is preferably 0.1 to 10 μm on average. This is because mixing becomes easy when the powder of the functional substance and a glass powder having the particle size in this range are mixed. Further, the viscosity in the paste state is preferably 200 to 300 Pa·s. This is because the viscosity of this range is suitable for application in screen printing and the like.

The content of the functional substance is preferably 0.5 to 70% by weight in a hardened state after baking, and more preferably 40 to 60% by weight. This is because in the case where the content of the functional substance is too small, the effect of preventing a decrease of the ozone concentration becomes insufficient although fixing strength of the functional substance onto the surface of the dielectric is sufficient, and in the case where it is too large on the contrary, the fixing strength of the functional substance onto the surface of the dielectric decreases although there is no problem in the effect of preventing a decrease of the ozone concentration.

The film thickness of the functional film consisting of a mixture of the functional substance and the fixing agent is preferably 0.1 to 20 μm in a hardened state. In the case where the film thickness is too thin, there is a risk that the effect of preventing a decrease of the ozone concentration is insufficient, and on the contrary, in the case it is too thick, uniformity of the film thickness distribution decreases, and it becomes difficult to make the gap amount in the discharge gap uniform.

The dielectric is preferably a high purity ceramic, and especially preferably an alumina sintered plate with a purity of 80% or more, 90% or more, particularly 95% or more, and more particularly an alumina sintered plate of 99% or more is preferable. A purpose of using the alumina sintered plate is to secure cleanliness due to ozone resistance and sputtering resistance.

The thickness of the dielectric is preferably 0.05 to 1 mm. When it is too thin, the voltage resistance value becomes low, and securing of the necessary mechanical strength becomes difficult. In the case where it is too thick, the distance between the electrodes becomes large, and the discharge voltage becomes high.

Use of a conductive plate as the electrode structure is common. However, a film in which the electrode is formed on the surface of the anti-discharge gap side of the dielectric as a thin film is also preferable from the viewpoing of preventing abnormal discharge. The material of the electrode film includes Cu, Ag, Al, and Au. The thickness of the electrode film is preferably 5 to 70 μm. When it is too thin, heat is generated at a narrow part of the pattern width, and there is a fear that breaking of a wire occurs. In the case where it is too thick, there are many technical problems, and the formation of a uniform film thickness is difficult. Metal foil adhesion, sputtering, vapor deposition, flame spraying, screen printing, or the like is preferable as the forming method of the electrode film from the viewpoint of making the film thickness uniform.

Because a functional substance for preventing a decrease of the ozone concentration is fixed on the surface of the dielectric using a baking fixing agent in the discharge cell for an ozonizer in the present invention, a highly concentrated functional substance that is difficult to be contained in the dielectric can be made to exist on the surface of the dielectric, and the cell is superior in the effect of preventing a decrease of the ozone concentration by the functional substance. Because of this, the ability of the ozonizer can be brought to full without adding nitrogen into oxygen gas or with adding a small amount of nitrogen. On top of that, because the dielectric is not processed, a less expensive product on the market and a general-purpose material can be used as the dielectric, and a cell cost can be kept low. Furthermore, being different from the formation of the functional film with flame spraying and welding, because film fixing strength is high, peeling and falling-out can be prevented during a cell operation. Further, a film forming coat is less expensive, and from this respect, a cell cost can be kept low. Furthermore, film thickness control is easy, formation of a very thin film with a thickness of a few μm is possible, and there is no risk of having a harmful influence on a rib for forming a discharge gap.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic cross-sectional view of the discharge cell for an ozonizer showing one embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In the following, an embodiment of the present invention is explained based on the drawing. FIG. 1 is a schematic cross-sectional view of the discharge cell for an ozonizer showing one embodiment of the present invention.

The discharge cell for an ozonizer in this embodiment is equipped with plate-shaped dielectrics 10, 10 which are arranged in parallel at a prescribed space therebetween. The dielectrics 10 consist of a high purity alumina sintered substrate available from the market.

A seal part 11 and a rib 12 are provided on opposing surfaces of the dielectrics 10, 10 in order to form a discharge gap 20 with a prescribed gap between the opposing surfaces. These consist of a glass sintered material, the seal part 11 is located at a peripheral part between the counter surfaces, a plurality of the ribs 12 are provided inside of the seal part 11, the dielectrics 10, 10 are bonded and unified with a prescribed space between them by bonding the ribs that are corresponding to each other with a glass sealing agent 13, and the discharge gap 20 of which the circumference is sealed is formed between the opposing surfaces.

The seal part 11 and the rib 12 are provided on both opposing surfaces of the dielectrics 10, 10 here. However, they may be provided on one of the surfaces.

The discharge gap 20 is connected to a raw material gas flow path and an ozone gas flow path formed in the perpendicular direction to the peripheral part of the dielectrics 10, 10. A smaller gap amount of the discharge gap 20 is better in order to make the purity of ozone gas high, specifically 200 μm or less is preferable, more preferably 100 μm or less, and especially preferably 50 μm or less.

A functional film 14 is provided farther inside than the seal parts 11, 11 of the opposing surfaces of the dielectrics 10, 10 together with the rib 12. The functional film 14 is a thin film formed by fixing a fine powder of the catalytic substance like TiO₂ that hinders a decrease of the ozone concentration on the counter surface in a film form by a baking fixing agent consisting of glass, and formed on a part excluding the rib 12 that is farther inside from the seal part 11. A step of forming the functional film 14 is normally before bonding the dielectrics 10, 10 and after forming the seal part 11 and the rib 12. However, the seal part 11 and the rib 12 can be formed at the same time. The film thickness of the functional film 14 is sufficiently smaller than the height of the seal part 11 and the rib 12, and is a few μm.

On the surface of the anti-discharge gap side (back side) of the dielectrics 10, 10, film-formed electrodes 30, 30 are formed individually with metal foil adhesion remaining on the peripheral part in a frame form, a high frequency high voltage power supply 40 is connected to this. The one terminal of the power supply 40 is grounded, the electrode 30 connected to this terminal is a low voltage electrode, and the other electrode 30 is a high voltage electrode.

On farther back side of the dielectrics 10, 10, a plate-shaped cooling body or the like is provided through an insulating plate, and with this, a discharge cell unit is configured. The plate-shaped cooling body may be a ceramic plate the same as the dielectric 10, or it may be a metal plate. Any cooling body has a configuration in which a coolant circulates inside in the direction parallel to the plate surface. Then, a discharge cell for an ozonizer is formed by layering such a discharge cell unit in the thickness direction.

In the operation of the ozonizer, high purity oxygen gas is supplied to the discharge gap 20 of the discharge cell as a raw material gas. The purity of the oxygen gas is preferably 99.9% or more from the viewpoint of cleanliness or the like, and especially preferably 99.99% or more. Further, a prescribed high frequency high voltage is applied between the electrodes 30, 30 to generate silent discharge in the discharge gap 20. Furthermore, cooled water as the coolant is supplied in the cooling body arranged on back side of the electrodes 30, 30.

The high purity oxygen gas circulating in the discharge gap 20 is exposed to the silent discharge, ozonized, and ozone gas is produced. Because a high purity alumina sintered substrate is used in the dielectrics 10, 10 and high purity oxygen gas is used as a raw material, normally the original performance of the ozonizer is not exhibited, and the ozone concentration of the ozone gas is low. However, because the functional film 12 containing a large amount of the catalytic substance such as TiO₂ is formed on the opposing surfaces of the dielectrics 10, 10 and a large amount of the catalytic substance is exposed to the discharge gap 20, high purity ozone gas is produced.

EXAMPLES

Next, an advantage of forming the functional films 14, 14 on the opposing surfaces of the dielectrics 10, 10 is explained using a case where the catalytic substance in the functional films 14, 14 is TiO₂ and NiO.

In the above-described discharge cell for an ozonizer, a high purity alumina powder sintered substrate with a purity of 99.5% available from the market was used as the dielectric. The thickness is 0.5 mm. The area of the discharge gap is 100 cm², and the gap amount is 0.1 mm (100 μm). Oxygen gas with a purity of 99.99% or more was supplied as a raw material gas with a flow rate of 1 L/min and a pressure of 0.2 MPa. Power supply was set to be the maximum power of the ozonizer. The ozone concentration of the produced ozone gas was 10 g/m³ (N) and was extremely low compared with the objective ozone concentration 200 g/m³ (N).

0.5 vol % of nitrogen gas was added to the above-described high purity oxygen gas. However, the ozone concentration was still 10 g/m³ (N). That is, the effect of adding nitrogen gas was not realized.

A functional film was formed on a part excluding the rib inside of the seal part on the dielectric counter surface with the following method. Three types of metal oxide powders of TiO₂, NiO and WO₃ and three types of metal powders of Ti, Ni and W were used as the functional substance. The maximum particle size of the oxide powder is 5 μm. Although some of the metal powders have a particle size larger than 5 μm, there is no adverse effect on formation of the functional film because the large particle size is reduced during the mixing process. The baking fixing agent is SiO₂—Al₂O₃—B₂O₃ glass, it satisfies SiO₂: 60 to 70% by weight, Al₂O₃: 1 to 10% by weight, and B₂O₃: 10 to 20% by weight, and the particle size is about 3 μm in average.

A mixture of a functional substance powder and a glass powder was made to be a solid, and it was made to be a paste by adding a vehicle. The compounded ratio and paste viscosity are shown in Table 1. That is, the compounded ratio of the solid to vehicle was 60:40 in % by weight, and there were three types of compounded ratios of the functional substance powder to the glass powder in the solid that were 18:42 (3:7), 24:36 (2:3), and 30:30 (1:1). That is, an amount of the functional substance in the solid was very large and being 30% by weight, 40% by weight, and 50% by weight, and it was a level that cannot be contained in an alumina sintered substrate.

TABLE 1 CONDI- TION 1 CONDITION 2 CONDITION 3 FUNCTIONAL 18 24 30 SUBSTANCE POWDER (wt %) GLASS POWDER (wt %) 42 36 30 VEHICLE (wt %) 40 40 40 PASTE TiO₂ 260 275 300 VISCOSITY NiO 230 240 245 (Pa · s) WO₃ 205 220 260 Ti 206 221 240 Ni 224 243 255 W 218 239 250 OZONE TiO₂ 198 253 320 CONCENTRA- NiO 172 215 288 TION WO₃ 173 201 226 (g/m³ N) Ti 230 244 263 Ni 120 173 198 W 174 202 208

After forming the seal part and the rib, the paste prepared in such a manner was screen-printed in a thickness of about 15 μm on a part excluding the seal part and the rib on the surface of the above-described alumina substrate, and it was baked with a condition of 850° C. for 10 minutes. The vehicle in the paste was removed by baking, and a functional film in which the functional substance powder was fixed by the glass was formed on a part excluding the seal part and the rib on the surface of the alumina substrate. The thickness of the functional film was about 9 μm. Each height of the seal part and the rib was made a little larger so that 0.1 mm (100 μm) as the gap amount of the discharge gap was secured. The formed functional film attached firmly on the substrate surface and the film itself fixed the oxide powder firmly in spite that it contained a large amount of the catalytic substance.

Moreover, the seal part and the rib were formed by mixing a glass powder (SiO₂: 60 to 70% by weight, Al₂O₃: 1 to 10% by weight, and B₂O₃: 10 to 20% by weight) and an alumina powder, applying the mixed powder that had been made into a paste by mixing a binder, and baking with a condition of 850° C. for 10 minutes. The height of the film formed with one time application and baking was about 25 μm, and the application and baking were repeated until the prescribed height is secured. The re-melt temperature after baking as a characteristic of a baked glass was considerably higher than the baking temperature. Because of this, there was no risk of softening and melting of the seal part and the rib part that had been formed in advance in the formation of the seal part and the rib and furthermore the formation of the functional film.

A discharge cell for an ozonizer was assembled using the produced dielectric, and the ozonizer was operated with the same condition as described above. The ozone concentration is written down in Table 1. In the case of any dielectrics, either the objective ozone concentration [200 g/m³ (N)] was secured or an ozone concentration closer to the objective was secured although the objective was not secured, and an ozone concentration exceeding 300 g/m³ (N) at the highest was observed. Further, the contami was not observed in the produced ozone gas. 

1. A discharge cell for an ozonizer in which a dielectric is arranged contacting at least one electrode in order to form a discharge gap for generating ozone between a pair of electrodes, wherein a functional substance to hinder a decrease of the ozone concentration is fixed on the surface of the dielectric by a baking fixing agent showing ozone resistance and sputtering resistance under the production of ozone in the discharge gap.
 2. The discharge cell for an ozonizer according to claim 1, wherein the functional substance is Ti, W, Sb, Mn, Fe, Co, Ni, V or Zn, or an oxide of these metals (MxOy).
 3. The discharge cell for an ozonizer according to claim 1, wherein the baking fixing agent is a glass that becomes a paste form that is capable of powder kneading the functional substance and attaching to the surface of the dielectric, fixes the functional substance on the surface of the dielectric by hardening by baking, and shows ozone resistance and sputtering resistance under the production of ozone in the discharge gap.
 4. The discharge cell for an ozonizer according to claim 3, wherein the glass is SiO₂—Al₂O₃—B₂O₃ based and satisfies SiO₂: 60 to 70% by weight, Al₂O₃: 1 to 10% by weight, and B₂O₃: 10 to 20% by weight.
 5. The discharge cell for an ozonizer according to claim 1, wherein the dielectric is an alumina sintered plate with a purity of 80% or more. 